linux-kernel - Re: [PATCH v1] scsi: ufs-mediatek: Enable UFSHCI_QUIRK_SKIP_MANUAL_WB_FLUSH

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Message-ID: <5eb12622222bd9ba5e705801a204f3160ba3966b.camel@gmail.com>
Date:   Thu, 24 Dec 2020 13:01:43 +0100
From:   Bean Huo <huobean@...il.com>
To:     Avri Altman <Avri.Altman@....com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Can Guo <cang@...eaurora.org>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "alim.akhtar@...sung.com" <alim.akhtar@...sung.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "bvanassche@....org" <bvanassche@....org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuohong.wang@...iatek.com" <kuohong.wang@...iatek.com>,
        "peter.wang@...iatek.com" <peter.wang@...iatek.com>,
        "chun-hung.wu@...iatek.com" <chun-hung.wu@...iatek.com>,
        "andy.teng@...iatek.com" <andy.teng@...iatek.com>,
        "chaotian.jing@...iatek.com" <chaotian.jing@...iatek.com>,
        "cc.chou@...iatek.com" <cc.chou@...iatek.com>,
        "jiajie.hao@...iatek.com" <jiajie.hao@...iatek.com>,
        "alice.chao@...iatek.com" <alice.chao@...iatek.com>
Subject: Re: [PATCH v1] scsi: ufs-mediatek: Enable
 UFSHCI_QUIRK_SKIP_MANUAL_WB_FLUSH_CTRL

On Thu, 2020-12-24 at 11:03 +0000, Avri Altman wrote:
> > > Do you see any substantial benefit of having
> > > fWriteBoosterBufferFlushEn
> > > disabled?
> > 
> > 1. The definition of fWriteBoosterBufferFlushEn is that host allows
> > device to do flush in anytime after fWriteBoosterBufferFlushEn is
> > set as
> > on. This is not what we want.
> > 
> > Just Like BKOP, We do not want flush happening beyond host's
> > expected
> > timing that device performance may be "randomly" dropped.
> 
> Explicit flush takes place only when the device is idle:
> if fWriteBoosterBufferFlushEn is set, the device is idle, and before
> h8 received.
> If a request arrives, the flush operation should be halted.
> So no performance degradation is expected. 

Hi Stanley

Avri's comment is correct, fWriteBoosterBufferFlushEn==1, device will
flush only when it is in idle, once there is new incoming request, the
flush will be suspended. You should be very careful when you want to
skip this stetting of this flag.

Bean